In vitro studies in cell culture have demonstrated the inappropriate expression of the c-sis/PDGF-2(B) proto-oncogene by responsive human malignant cell lines derived from human tumors of mesenchymal origin, such as glioblastomas, fibrosarcomas and osteosarcomas. These findings suggest the possibility that the inappropriate expression of the c-sis proto- oncogene may be part of the mechanisms that lead certain normal cells of mesenchymal origin towards malignancy. These studies were performed in cell culture, in vitro, using established cell lines. We now propose to extend these studies in vivo, in primary human tumors and in primary cell cultures derived from the tumors. We have selected for this purpose primary human astrocytomas which are the focus of ongoing investigations. Our objective is to investigate the expression of PDGF and PDGF receptor genes in these primary tumors, along with the coordinate expression of "progression" growth factor genes (IGF's, TGF-alpha). In vitro and in vivo studies indicate that PDGF alone cannot adequately account for stimulation of optimal cell growth. The co-ordinate expression of PDGF and "progression" growth factors may be a necessary step contributing to the development and maintenance of the astrocytoma tumors. Gene expression will be demonstrated using Northern and/or dot blot analysis. Identification of the cells of origin in the primary tumors expressing the genes and their protein products will be accomplished using in situ hybridization and immunocytochemistry. We anticipate that these studies will provide an insight on these important molecular events. Furthermore, they may contribute to new approaches for the detection of astrocytomas, using for this purpose the expression of c-sis mRNA as a molecular probe. Cell heterogeneity of primary cultures derived from the primary tumors and to subclone their heterogeneous cell population; and to correlate the growth characteristics of the subclones with molecular basis for the characterization of cell heterogeneity, using as molecular markers the expression of specific growth factor genes and their protein products. We anticipate that variations in cell types and in their growth characteristics will reflect the expression or co-expression of growth factors.